The present invention relates to a hydraulic circuit connected to an injector for injecting coiled tubing into a well, and a method of controlling the gripping of the tubing associated therewith.
Many coiled tubing injectors utilize a hydraulic circuit to control movement of one or more components of the injector in order to grip and advance the coiled tubing through the injector and to the well.
Several potential problems arise during the operation of a typical injector hydraulic circuit. In particular, if the diameter of the tubing increases during the operation of a typical injector hydraulic circuit, there may be an unsafe pressure increase in the circuit. Also, many injector hydraulic circuits require a human operator to move near the injector during operation to adjust the gripping pressure on the tubing, thus increasing the risk of harm to the operator.
Further, if there is a loss of pressure to the injector hydraulic circuit, the tubing will be released, thus creating a “runaway” situation whereby the released tubing could cause harm to the operator and significantly damage the injector and the well. Current runaway-prevention solutions include using a shut-off valve to isolate the injector hydraulic circuit after a loss of pressure, or connecting a check valve upstream of the injector hydraulic circuit to hold the pressure in the injector hydraulic circuit. Although these solutions prevent a complete loss of pressure to the injector hydraulic circuit, they do not provide an easy and safe way for the human operator to resume control of the injector hydraulic circuit after the pressure has been restored. In addition, neither of these solutions enables the gripping pressure on the tubing to be increased in the event of an unforeseen failure in operator-house pressure.
Therefore, what is needed is an injector for advancing coiled tubing into a well that overcomes these problems.